Black tea gets its colour, flavour, and health properties from a cascade of chemical reactions. During full oxidation, the green leaf's colourless catechins are enzymatically converted by polyphenol oxidase into the orange-red theaflavins (bright, brisk) and the brown-black thearubigins (depth and body). Caffeine content averages 40-70 mg per cup. Understanding these compounds explains why brewing temperature and steeping time matter so much.
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